Comparison of single-walled carbon nanotube growth from Fe and Ni nanoparticles using quantum chemical molecular dynamics methods

Metal-catalyzed SWCNT growth has been modeled using quantum chemical molecular dynamics (QM/MD) in conjunction with feeding of carbon atoms to C40–Fe55 and C40–Ni55 model complexes at 1500 K. The rate of Fe55-catalyzed SWCNT growth determined in this work was 19% slower than the Fe38-catalyzed growth rate. Conversely, Ni55-catalyzed SWCNT growth exhibited a growth rate 69% larger than of Fe55-catalyzed SWCNT growth, a fact consistent with excellent performance of Ni in laser evaporation and carbon-arc experiments. Ni55-catalyzed growth was preceded by the formation of extended polyyne chains at the base of the SWCNT, and so differed fundamentally from Fe55-catalyzed growth. These polyyne chains usually persisted for 10–30 ps. Subsequent polyyne ring condensation resulted in carbon polygon addition at the SWCNT base. The relative stabilities of the Cn carbon cluster moieties on the Fe55 and Ni55 surfaces were consistent with the relative strengths of the Fe–C, Ni–C and C–C interactions. The presence of smaller carbon moieties on the Fe55 surface led to the dissemination of surface iron atoms, and subsequent diffusion of short Cn units through the subsurface region of the catalyst particle. Conversely, the Ni55 catalyst particle was observed to be more stable, remaining intact to a greater extent.